What “Check Injection System” Means on Your Car

It’s a dashboard warning that the engine control unit has detected a fault in the fuel/air injection and emissions system—often related to injectors, fuel pressure, sensors, EGR/DPF components, or wiring. While the car may still run, continued driving can cause damage or trigger limp mode; read fault codes and seek diagnosis promptly.

What the Warning Covers

The message “Check Injection System” is common on many European cars—especially modern diesels from Renault, Peugeot/Citroën, Opel/Vauxhall, and others—but the meaning is similar across brands. It is a catch‑all alert for issues affecting how fuel and air are measured and delivered to the engine or how exhaust emissions are treated.

Common Triggers

Multiple systems can set off this warning. The underlying cause ranges from simple sensor faults to mechanical fuel-pressure problems.

• Low fuel rail pressure: clogged fuel filter, weak/high-pressure pump, leaking lines
• Faulty or leaking fuel injector(s), or injector coding/adaptation errors
• Fuel rail pressure sensor or wiring faults
• Airflow/boost issues: MAF or MAP sensor failure, intake or boost hose leaks, turbo underboost
• EGR valve stuck or clogged passages affecting combustion and emissions
• DPF problems: soot overload, failed differential pressure sensor, regeneration not completing
• Combustion detection issues: crankshaft/camshaft position sensor faults, misfires (gasoline)
• Glow plug or glow plug relay faults (diesel cold-start impact)
• Contaminated/bad fuel or water in diesel
• Low system voltage/weak battery causing sensor and pump anomalies
• Outdated engine control software requiring an update

The breadth of possible causes is why the message is generic; a scan tool and data checks are needed to pinpoint the fault.

Symptoms You Might Notice

Drivers often see the message alongside one or more noticeable changes in how the car runs.

• Reduced power or “limp mode,” poor acceleration
• Rough idle, hesitation, or hard starting (especially when cold)
• Excess smoke from the exhaust (black, white, or blue)
• Worse fuel economy or strong diesel smell (possible leak)
• Engine warning light on steadily or flashing; cooling fans running unexpectedly
• Frequent or failed DPF regenerations on diesels

Any combination of these symptoms strengthens the case for immediate diagnosis to prevent secondary damage.

What You Should Do Immediately

Your next steps depend on how the car behaves and whether the warning is steady or accompanied by severe symptoms.

• If the warning is steady and the car drives normally: reduce load and speed; avoid hard acceleration and towing.
• If there’s severe power loss, knocking, heavy smoke, fuel smell, or a flashing warning: pull over safely and consider recovery; continued driving risks engine, turbo, catalyst, or DPF damage.
• Check simple items: ensure the fuel cap is tight; note recent refueling (possible bad fuel); verify you used the correct fuel.
• Scan for OBD-II codes with a reader or at a shop; record codes and freeze-frame data before clearing.
• If under warranty or with an active service campaign, contact the dealer; some issues are software-related.

Prioritizing safety and early diagnosis typically reduces repair cost and prevents collateral damage.

How a Mechanic Will Diagnose It

Professionals follow a structured process to isolate the fault without replacing parts unnecessarily.

1. Scan the ECU for diagnostic trouble codes (DTCs) and review freeze-frame data.
2. Check live data: fuel rail pressure (commanded vs. actual), injector corrections, MAF/MAP readings, boost, lambda/O2, DPF differential pressure and soot load, EGR position.
3. Perform visual and smoke/pressure tests for intake and boost leaks; inspect fuel lines for leaks/air ingress.
4. Fuel system tests: filter restriction, low-pressure supply, high-pressure pump output, and injector leak-off/balance.
5. Electrical tests: sensor power/ground, signal integrity, continuity for suspect circuits.
6. For diesels: assess DPF condition; if appropriate, complete a controlled regeneration after fixing root causes.
7. Check for technical service bulletins (TSBs) and apply ECU software updates if indicated.
8. Road test to confirm that parameters are in range and the fault does not return.

This step-by-step approach prevents misdiagnosis and helps ensure that a single underlying fault is correctly addressed.

Typical Fault Codes Linked to This Message

While codes vary by brand, these are frequently associated with a “Check Injection System” alert.

• P0087/P0088: Fuel rail/system pressure too low/high
• P0190–P0193: Fuel rail pressure sensor circuit/performance
• P0201–P0204 (and higher): Injector circuit faults; P02XX range for contribution/balance
• P0101/P0102: MAF sensor performance/low input
• P0299: Turbocharger underboost
• P0401/P0402: EGR flow insufficient/excessive
• P2452/P2453/P2463: DPF differential pressure sensor/soot accumulation
• P0335/P0340: Crankshaft/camshaft position sensor faults
• P0670/P0671–P0674: Glow plug control/module and individual plugs (diesel)
• P0121: Throttle position sensor performance (gasoline and some diesels)

The exact code narrows the cause dramatically and guides targeted testing.

Estimated Repair Costs and Time

Costs vary by vehicle, engine type (diesel typically higher), and region. Ballparks (parts + labor):

• Fuel filter: $50–$200, 0.5–1.0 hour
• MAF/MAP sensor: $100–$400, 0.5–1.0 hour
• Fuel rail pressure sensor: $150–$350, 0.7–1.5 hours
• Injector testing/replacement (diesel): $250–$600 each + coding; 1–3 hours per injector
• High-pressure fuel pump: $800–$2,000+, 3–6 hours
• EGR clean/replace: $200–$1,000, 1–4 hours
• DPF clean: $300–$600; DPF replacement: $1,500–$3,000+
• Boost hose/intercooler repair: $50–$600, 0.5–3 hours
• ECU software update: $0–$200, 0.3–1.0 hour
• Diagnostic evaluation: $100–$200 typically credited if repairs proceed

A thorough diagnosis up front often prevents unnecessary parts replacement and controls costs.

How to Reduce the Chance of a Repeat

Good maintenance and driving habits can prevent many injection-system warnings.

• Use high-quality fuel; avoid running very low on fuel
• Replace the fuel filter on schedule; drain water separators on diesels if equipped
• Maintain a healthy battery and charging system to stabilize sensor readings
• For turbo engines: gentle warm-up and cool-down; fix boost leaks promptly
• For DPF-equipped diesels: include regular highway drives to allow passive/active regenerations
• Use the correct low-ash oil for DPF systems; keep up with oil changes
• Address early symptoms (rough idle, smoke, warning lights) before they escalate
• Keep connectors dry and secure; corrosion can mimic sensor failures

Preventive care reduces both the likelihood and severity of injection-related faults.

Brand-Specific Notes

The message text differs by manufacturer, but the implications are similar.

• Renault/Nissan dCi: “Check Injection System” often relates to EGR/DPF, boost leaks, rail pressure, or injector coding
• Peugeot/Citroën (Stellantis): “Engine fault: repair needed” or “Anti-pollution fault” covers injection and emissions components
• Opel/Vauxhall: Similar injection/emissions warnings tied to rail pressure and DPF systems
• VW/Audi, BMW, Mercedes: Typically display a check engine or emissions warning; sub-messages point to DPF or AdBlue/DEF systems on newer diesels

Always consult the owner’s manual for your model’s exact wording and guidance, and check for TSBs or recalls.

When It’s Safe to Drive

Whether you can continue depends on the severity of symptoms and risk of damage.

• Generally safe for short distances: steady warning, normal drivability, no smoke or overheating
• Not safe: flashing warning, severe power loss, loud knocking, heavy smoke, fuel smell/leak, overheating
• If in doubt, arrange a tow to avoid costly damage to the engine, turbo, catalytic converter, or DPF

Err on the side of caution if the car’s behavior changes noticeably or multiple warnings appear together.

Summary

“Check Injection System” indicates a detected fault in fuel delivery, air metering, or emissions control—ranging from sensor issues to injector, pump, turbo, EGR, or DPF problems. Drive gently if the car behaves normally, but prioritize an OBD-II scan and professional diagnosis. Addressing the root cause early avoids expensive damage and restores performance and reliability.